U.S. Pat. No. 5,937,835 and its counterpart JP-H11-62724-A, for example, discloses a conventional motor-operated valve assembly, which drives an valve member to open and close a fluid passage. The motor-operated valve assembly is incorporated in an exhaust gas recirculation (EGR) system for recirculating an exhaust gas from an exhaust passage to an intake passage of a diesel engine, for example.
In the motor-operated valve assembly according to U.S. Pat. No. 5,937,835, a speed reduction mechanism transmits driving force to actuate its valve member. That is, a gear train transmits the driving force of an electric motor. The driving force is transmitted via a sector gear and a cylindrical protruding portion to a valve assembly. The rotational driving force of the electric motor is transformed into a driving force to reciprocate the valve assembly in its axial direction in this manner. As a result, the valve assembly reciprocates in the axial direction to open and close a fluid passage.
However, in the motor-operated valve assembly shown in U.S. Pat. No. 5,937,835, the valve assembly is located outside a motor gear and the gear train. That is, the valve assembly is arranged at an opposite side from an output shaft of the electric motor with respect to the gear train. Thus, a support portion, which supports the valve assembly slidably in the axial direction, is located at an opposite side from the electric motor with respect to the gear train, to upsize a body size of the motor-operated valve assembly. Further, the support portion for supporting the valve assembly is separately located at an opposite side from the electric motor with respect to the gear train in an actuator housing. Thus, the actuator housing requires an enough stiffness to form the support portion. As a result, a wall thickness of the actuator housing becomes large to upsize the body side of the actuator housing.